Method for heat-treating hollow articles



July 11, 1950 F.,G. TRITT ETAL METHOD FOR HEAT-TREATING HOLLOW ARTICLES Filed Dec 30, 1947 RUE/ 722295 Paws"? 5' E277 guns/a E Phi/X 5 ymutuymzn Patented July 11, 1950 ART ICLES Forest G. Tritt, Barberton, and Donald R. Phillips, Canal Fulton, Ohio, assignors to The B. F. Goodrich Company, New York, N. Y., a corporation of New York Application December 30, 1947, Serial No. 794,602

' 9 Claims. (01. 1853) This invention is concerned with a method for heat-treating hollow articles and is particularly concerned with a method for heat-treating inflatable hollow articles such as rubber boats and the like by heating the articles unconfinedly in an inflated condition with means being provided to prevent rupture thereof.

Large collapsible rubber articles such as rubber boats, pontons and the like are not readily made by molding because of their large size, such articles being fabricated from a plurality of sectional components. Furthermore, the size of such articles makes it desirable to vulcanizethe fabricated article in a vulcanizing chamber or autoclave rather than in a closely confined form. Such articles have heretofore been vulcanized While inflated, with elaborate means being provided for regulating the pressure diiferential between the inside and outside of the article to prevent rupture of the Walls during vulcanization.

It is an object of this invention to provide a method for heat-treating large hollow inflatable articles in the inflated condition without danger of rupturing the walls of the article. It is a further object of this invention to prevent an excessive pressure differential tending to rupture the walls of the article without the use of elaborate regulatory means. Other objects will be apparent from the description which follows.

In accordance with this invention, the method for heat-treating a hollow article having a Wall orifice comprises introducing into the article material adapted to undergo gaseous expansion when heated, capping the orifice with a closure member, preferably inflatable and of substantially less strength than the walls of the article, supporting the article unconfinedly in a heating space, and applying heat to the article whereby the article becomes fully inflated. The closure member inflates somewhat to aid in relieving internal pressure in the article and ruptures when the pressure differential inside and outside the article exceeds the rupturing strength of the member, thus preventing rupture of the walls of the article.

The invention is best described with reference to the vulcanization of a rubber boat by the preferred method. The single figure'of the accompanying drawing is a schematic representation of a boat being vulcanized in a steam chamber in accordance with the invention.

A rubber boat I is fabricated by cementing together a plurality of sectional members of a vulcanizable rubber composition or of fabric coated with such a composition. The boat, in general, comprises an annular inflatable tube H forming the sides of the boat with a sheet of rubberized fabric across the opening on one face of the tube forming a bottom I 2 for the boat. The tube II is provided with a wall orifice 13 having an outwardly extending nipple valve [4 for inflating and deflating the tube.

The. unvulcanized boat, which possesses a degree of structural strength, is then partially inflated with air, preferably to about half its normal capacity. The orifice I3 is capped by placing over the nipple M an inflatable rubber balloon or finger-cot l5 which serves as a distensible closure. The balloon or finger-cot preferably has a neck opening whose diameter is less than that of. the nipple M so that it must be stretched in order to be positioned over the nipple. In this way, the closure maintains itself in position on the nipple l4 without the necessity for auxiliary fastening means.

The closure I5 has substantially less bursting strength than the walls of tube I and preferably exhibits less resistance to inflation. It is desirable that the closure be capable of being inflated to at least several times its normal size to provide auxiliary capacity to accommodate the expansion of the air in tube ll.

Boat I0 is placed on a support rack 16 on a heater truck H, by which means the boat is supported unconfinedly to allow inflation thereof. The truck I! is moved into steam vulcanizer l8 which is provided with a steam inlet l9 and outlet 20, the inlet I9 being connected to a source of superheated steam not shown.

With the boat in position in the vulcanizer, the vulcanizer is closed and steam is blown into the vulcanizer chamber through inlet I9. The steam is introduced under pressure until a pressure of 35-40 pounds is attained, which pressure is maintained for a period of 15-30 minutes. The vulcanizing cycle may, of course, be varied in accordance With Well-known vulcanizing practices, that is, it may be desirable to increase the pressure and decrease the time or to decrease the pressure and increase the time of vulcanization.

When the steam is introduced into the vulcanizer. the air in the boat expands to fully inflate tube II to an unwrinkled condition. The pressure in the chamber tends to counteract the inflation caused by the expansion of gas in the tube. Since the tube originally is inflated to only half its capacity, the pressure differential be tween the tube and the chamber is just enough to keep the boat fully inflated during the heating and that in the chamber which pressure would rupture the walls of the boat if no reliefv means were provided. By means of this invention, however, the closure either blows ofi the valve or ruptures before rupture of the tubewall. In this way, the pressure differential is always kept. below the rupturing strength of the tube wall without the use of elaborate pressure regulating means and the boat is vulcanized While inflated so that there are no wrinkles in the finished article.

The method may be varied within the scope of the invention. The vulcanization may be carried out by hot air at atmospheric pressure if desired. In such a case, the original inflation of the boat should be somewhat less than half the normal capacity of the boat to prevent rupture of the closure during the heating cycle The boat is preferably partially inflated with a gas, but the inflation may be accomplished by introducing therein solid or liquid .material which will undergo gaseous expansion under vulcanizing conditions. Thus, a small amount of water may be introduced into the tube or a more volatile liquid such as carbon tetrachloride may be used, as well as heat decomposable solid materials such as ammonium compounds, carbonates, bicarbonates, amines, etc. It is sometimes desirable to use such. liquid or solid materials, particularly when high pressure steam is' used for vulcanization, because such materials expand slowly and the boat does not become fully inflated until the requisite pressure is obtained in the vulcanizing chamber. In some cases, as where water is introduced into the boat, it is desirable to introduce, in addition, a small amount of a rubber latex which serves to seal any pin holes in the tube.

phragm or closure preferably comprises rub-, r

her or rubbery material so as to be expansible and preferably has less resistance to expansion than the tube wall. The diaphragm may be fastened to the nipple in any desired manner or may be merely stretched over the nipple when an elastic diaphragm is usedso that the diaphragm blows of!" the nipple rather than ruptur' ing when the pressure in the tube becomes excessive. The diaphragm or closure may comprise a rubber balloon, a thin-walled rubber tube resembling a glove finger, a finger-cot or a similar expansible member.

The invention has been described in detail with reference to the vulcanization of a rubber boat. The method embodying the invention, however, is applicable for heat-treating any hollow inflatable article having a wall orifice and is particularly applicable for vulcanizing collapsible rubber articles of large size.

Variations and modifications may be effected in the method of heat-treating such articles within the spirit and scope of the invention as defined in the appended claims.

We claim:

1. The method of heat-treating an inflatable hollow article provided with a wall orifice, which method comprises introducing into said article material adapted to undergo gaseous expansion when heated, capping said orifice with an imperforate diaphragm having substantially less resistance to expansion than said article, supporting said article unconfinedly, and applying heat to the exterior of said article to cause inflation thereof with said diaphragm expanding to prevent rupture of said article.

2. The method of heat-treating an inflatable hollow article havinga wall orifice, which methodcomprises partially inflating said article with agas, capping.v the orifice of said article with an imperforate: expansible diaphragm of less strength than said article, supporting said article unconfinedly in a closed heating space, and applying-heat to said article while preventing rupture thereof by inflation of said diaphragm as a result, of expansion of the gas.

The method for heat-treating an inflatable hollow article havingv a wall orifice, which method comprisesintroducing into said article material adapted to undergo gaseous expansion when heated, closing said orifice with an inflatable closure having substantially less strength than said article, supporting said article unconfinedly in a closed heating space, applying, heat and. pressureto the exterior. of said. article causing gaseous' expansion of the. material in said article with inflation of the diaphragm and the articletendingto equalize the pressure inside and outside said article,. and thereafter reducing the pressure in said heating space torupture said diaphragm torelievepressure in said article.

4'. The method for heat-treating a collapsible hollowrubbery article-having a wall orifice, which method comprises partially inflating said article with a gas, capping said orifice with a rubbery balloon-like diaphragm having substantiall less resistance to inflation and substantially less bursting strength than said article, supporting said article unconfinedly in a closed heating space, applying heat and pressure to the exterior of said article causing expansion of the gas in said article tending to fully inflate the article with the diaphragm inflating to relieve excessive internal pressure, and thereafter rapidly reducing said external pressure during which reduction the diaphragm ruptures when the pressure differential between the inside and outside of said article exceeds the strength of said diaphragm.

5. The method of vulcanizing a collapsible rubher article havingawall orifice provided with an outwardly extending nipple, which method comprises providing an imperforate inflatable balloon-like rubber diaphragm having a neck opening normally smaller than said nipple, partially inflating said article with air, stretching said diaphragm neck and placing it over the nipple to close the orifice. supporting the article unconfined'ly in a closed heating space, introducing steam under pressure into said heating space to vulcanize the article with the air in said article expanding to inflate the article and with the diaphragm inflating to relieve excessive internal pressure in the article, and thereafter releasing the external pressure on said article to cause said diaphragm to blow off said nipple to prevent rupture of the article from an excessive pressure differential. V

6. The method of vulcanizing a collapsible rubber boat having a wall orifice provided with an outwardly extending" nipple, which method comprises providing an expansible rubber balloon,

5 partially inflating said boat with air, capping the nipple with said balloon, supporting the boat unconfinedly in a closed chamber, subjecting said boat to steam at a pressure of 35-40 pounds per sq. in. for 15-30 minutes, and thereafter releasing the steam pressure in the chamber to rupture the balloon to prevent a pressure difierential between the inside of the boat and the chamber sufficient to rupture the Walls of the boat.

'7. The method of vulcanizing an inflatable hollow article comprising vulcanizable material and having a wall orifice therein, which method comprises partially inflating said article with a fluid adapted to expand upon heating to the normal vulcanizing temperature, closing said wall orifice with a thin-walled elastic closure element having a bursting strength less than that of said article, supporting the unvulcanized article unconfinedly in a closed vulcanizing chamber, subjecting it to heat and pressure within said chamber to expand it to approximately a fully inflated condition and to vulcanize it, and releasing said heat and pressure from said chamber to open said closure element and to deflate the article.

8. The method of heat-treating an inflated hollow article having an inflation orifice while preventing overinflation thereof, which method comprises introducing into said article a material adapted to inflate said article upon heating, closing said orifice with an expansible rupturable closure member which will rupture at a lower internal pressure than will said article, and heating said article while unconfined to cause inflation thereof and bring about said heat treatment, said closure member expanding with moderate internal inflation pressure to relieve said pressure and rupturing to prevent development of excessive inflation pressure.

9. In a method of heat-treating an inflated hollow article having an inflation orifice while supported unconfinedly in a closed heating chamber and preventing overinflation thereof, the steps which comprise introducing into said article a substance adapted to expand said article when heated, closing said orifice with an imperforate expansible diaphragm which is rupturable at a lower inflatiOn pressure than is the body of said article, and heating said article in said chamber while supported unconfinedly, said diaphragm expanding with moderate inflation pressure to relieve said pressure and rupturing to prevent development of excessive inflation pressure.

FOREST G. TRITT. DQNALD R. PHILLIPS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,652,793 Perry Dec. 13, 1927 2,418,166 Dimore. Jr., et al. Apr. 1, 1947 2,428,944 Schrank Oct. 14, 1947 

